Last week I was watching a TV show. During a dialog, one character asked the other something like "So how long will it take you to do it" and the answer was simply "6 to 8 weeks".
This led me to believe Jeff was just using a known meme and just applying it here, over five years ago but all my searches utterly failed and pointed on this very meta post as the origin of the meme.
Searching just for 6 to 8 weeks without quotes or anything:
First out of nearly two billion results. Nice.
Searching for "6 to 8 weeks" with quotes, same just with less total results:
Then I found this post, an interview with ERIK WERNQUIST who is the creator of Crazy Frog:
How much time did it take in the beginning to program it?
The first animation I did at my spare time. I worked about 6 to 8 weeks on building the character and making the first animation
Coincidence, fate or something that Jeff read and later used himself? :)